The subject of the present invention is a device for closing, with a security seal, a container of a rigid material, such as glass, by means of a screw cap of rigid thermoplastics material.
A closure device of the type specified is known from the published European application EP-A-0261645 by the same Applicant.
This closure device is used for closing glass containers used in the food industry for products which, after their introduction into the container and the application of the screw cap, are intended to undergo heat-treatment at a fairly high temperature in order to pasteurise the product or create a vacuum within the container.
In the practical use of a closure device of the type specified above, it has been found that the cap may be subjected to partial unscewing from the position to which it was originally screwed by means of a screw-capping machine in order to achieve a degree of deformation of the sealing ring and ensure the seal.
This partial unscrewing is permitted by resilient extension of the weakened zones connecting the tear-strip to the skirt of the cap due to tensile stress, and is sufficient to compromise the seal of the sealing ring, with a consequent loss of the vacuum produced in the container which prejudices the long-term preservation of the food product in the container.
The unscrewing may, for example, be caused accidentally by a person handling a container displayed in a large shop.
The seal of the closure may also be compromised if, as a result of the incorrect adjustment of the screw-capping machine, the cap is overtightened when it is first screwed on to the container, whereby the sealing ring is damaged.
DE-A-2913883 discloses a device for closing a bottle for perfumes or the like by means of a screw cap of thermoplastics material, in which the bottle and the cap are of rectangular shape in plane view.
The cap is provided with a central internally threaded tubular portion having at its lower end two radially yielding segments each of which is provided on its inner surface with a central radial notch.
When the cap is screwed on the neck of the bottle, the two segments snap-engage beneath an annular rib of the neck and the central notch of each segment is engaged by a retaining rib which radially protrudes from the bottle neck under the annular rib, in order to ensure that in the screwed condition the flat side faces of the cap are flush with the corresponding side faces of the bottle and the cap is maintained in such angular position.
The closure disclosed in this document is not a tamper-proof closure, because the two segments of the cap do not form a security seal. Moreover each notch of the segments has a circumferential extent which corresponds to the circumferential extent of the respective retaining rib of the bottle, which would not allow correct screwing by means of a screw-capping machine of a cap having a sealing ring constituted by a plastisol poured in annular seat of the cap and polymerised by heating.